Yep ... Desert Captain nailed it above.
The first approach he mentioned above is what we do, except for one thing I describe in the next paragraph: After turning the air flow control to MIX so that cold air from the A/C comes out at the driver's and passenger's feet and windshield areas (so their feet and upper bodies are kept cool regardless of engine heat), I make sure that the A/C mode is set to MAX so that no outside air is used -> all air processed by the A/C is recirculated air from inside the interior. This makes the A/C way more effective since it is only processing already-cooled inside air instead of trying to continuously be cooling new hot air coming in from the outside.
The second approach suggested by D.C. we never do, because we keep the coach and cab completely closed up when traveling - no windows or vents open anywhere regardless of outside air temperatures. This goes along with keeping the A/C set to the MAX position so no outside air is used. The reason for this is to keep the RV's interior as clean as possible by blocking all dust that may be carried by any outside air when traveling.
2005 E450 Itasca 24V Class C